Compute Allowed Changes in Adding to or Dropping from a Formula
drop.scope compute those terms that can be
individually added to or dropped from a model while respecting the
hierarchy of terms.
- the terms or formula for the base model.
- the terms or formula for the upper (
add.scope) or lower (
drop.scope) scope. If missing for
drop.scopeit is taken to be the null formula, so all terms (except any intercept) are candidates to be dropped.
"factor"attribute of the terms of the base object.
- a list with one or both components
"factor"attribute of the lower and upper scopes respectively.
factor.scope is not intended to be called directly by users.
drop.scopea character vector of terms labels. For
factor.scope, a list with components
add, character vectors of terms labels.
add.scope( ~ a + b + c + a:b, ~ (a + b + c)^3) #  "a:c" "b:c" drop.scope( ~ a + b + c + a:b) #  "c" "a:b"